bio 12 chapter 6 metabolism notes

8/13/2019 Bio 12 Chapter 6 Metabolism Notes

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Biology 12 Chapter 6 Notes Package Page 1of 12(KWP)

Chapter 6 : MetabolismEnergy and Enzyme

6.1 Energy

Energy

Energy is the ability to do work or bring about a change Kinetic energyis the energy of motion Potential energyis stored energy Chemical energyin food is converted into mechanical energy when an animal moves

Two laws of Thermodynamics

1. The first law of thermodynamics states the energy cannot be created nor destroyed2. The second law states the energy cannot be changed from one form to another without

the loss of usable energy. As energy is converted from one form to another it eventuallybecomes heat which dissipates in the environment

Cells and Entropy

Entropyis a measure of disorder. To achieve the order in the organization of organismsthat requires an input of energy. Eventually this energy is converted to heat (high entropy)and dissipates. Therefore, a continual input of energy is necessary to maintain organisms

6.2 Metabolic Reactions and Energy Transformations

Metabolism InvolvesReactants

Metabolismconsists ofchemical reactions that usereactants and result inproducts. Free energyisthe energy available to dowork after a reaction Exergonic reactionsreleaseenergyExergonic


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Endergonic reactionshaveto have an input of energy inorder to occur

ATP: Energy for Cells:

Structure of ATP

Adenosine TriphosphateATP) ATP is adenine plus threephosphate groups. ATP is ahigh energy molecule becausethe third phosphate group iseasily removed.

Section 6.1~6.2 [Questions]

1) What is metabolism?

2) Under what conditions do reactions occur spontaneously?

Endergonic


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3) What is free energy? And how is it ' better' than entropy when consideringreactions?

4) Use - and + and mention which ones go with exergonic and endergonicreactions. Add in the correct letter and symbol for free energy.

5) What are some benefits of using ATP over glucose in terms of energy?

6) How are exergonic and endergonic reactions related to coupled reactions?Relate this to ATP.

7) What are 3 functions of ATP in terms of work?

8) What is a coupled reaction?


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6.3 Metabolic Pathways and Enzymes

Metabolic Pathways

Metabolic Pathwaysarelinked reactions thatbegin with a reactantand end with a product An enzymeis a

protein thatspeeds chemicalreactions becauseit causes

substrates toreact A pathway involving

A->B->C would requirean enzyme to help A ->B and another enzymeto help B->C


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Energy of Activation

Energy that must be added to cause molecules to react is called the energy ofactivation. (Ea) Enzymes lower the energy of activation, making it more likely thatsubstrates will meet

Enzyme - Substrate Complexes

The equation + + shows that the enzymeand substrateforma complex. Enzymes are named for their substrate because they are specific -the shape of the substrate are complementary to one another. A process calledinduced fitassures that an enzyme - substrate complex will form.

Exergonic

Endergonic


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Coupled Reactions

In coupled reactions, an exergonic reaction drives an endergonic reaction. Thebreakdown of ATP drives many coupled reactions.

Cellular Respiration

Photosynthesis


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Functions of ATP

ATP breakdown releases energy that drives reactions in cells, e.g., syntheticreactions, muscle contraction, nerve conduction

Factors Affecting Enzymatic Speed:1) Substrate Concentration

As substrate concentration increases, thereare more collisions between substratemolecules and enzyme

2) Temperature and pH

Both a warm temperature and an optimalpH speed an enzymatic reaction.

Usually a boiling temperature and an extreme pH cause a protein to denatureand the reaction stops


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3) Enzyme Concentration

When genes are active more enzyme is present to speed a reaction. Enzyme areoften activated when kinases phosphorylate them.

Nearly every enzymeactivity regulated byfeedback inhibition A product molecule

may occupy the activesite in competitiveinhibition


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The end product may alsobind to an allosteric site;when the end productoccupies this site, theshape of the active sitechanges and the substratecannot fit there and nomore product is formed.

Enzyme cofactorsinclude inorganic ioncofactors and non-

protein organiccoenzymes. Vitaminsare often componentsof coenzymes neededby enzymes to carryout their reactions.Coenzymes, unlikeenzymes, participate in thereaction

Homework questions:

1) Q: Draw a metabolic pathway that begins with a reactant, has 5

intermediate steps, and ends with a final product. Use letters and numbers tosymbolize your pathway. Include enzyme at each step.

A:

E1 E2 E3 E4 E5A -> B -> C -> D -> E -> F


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2) Q: What is the induced fit model of enzymes?A: It refers to the active site undergoing a slight change in order to accommodate itscorresponding substrate.

3) Q: Why are enzymes named for their substrate?A: This is to show their specificity. A specific enzyme is used to react with differentsubstrate.Examples:

Lipid Lipase

Urea Urease

Maltose Maltase

Ribonucleic acid Ribonuclease

Lactose Lactase

4. Q: Adding more substrate with a fixed amount of enzyme past a certainpoint no longer increases the rate of reaction. Why?A: When enzymes active sites are filled almost continuously with substrate, theenzymes rate of activity cannot increase any more. As a result, maximum rate hasbeen reached.

5. Q: Draw 3 graphs: label the Y axis with reaction rate and the X axis withsubstrate concentration, temperature and enzyme concentration. Then draw anappropriate graph and . (The rest is trivial).

A: Refer to graphs on P 4~5 of this note package.

6: Q: What is feedback inhibition, and how does it work? Discuss a simple andthen a more complicated example of it.A: Feedback inhibition occurs when the substrate is unable to bind to the active site ofan enzyme. The activity of almost every enzyme in a cell is regulated by feedbackinhibition.In the simplest case, when there is plenty of product, it binds to the enzymes activesite, and then the substrate is unable to bind. These are competitive inhibitors.In a more complex example, the end product of an active pathway binds to a site other

than the active site of the first enzyme. The binding changes the shape of the activesite and therefore the substrate is unable to bind to the enzyme, and the pathwayshuts down. Hence no more product is produced. These are non-competitive inhibitors.7. Q: Why do bacteria die yet humans do not when penicillin is administered?


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A: Penicillin is an antimicrobial agent that blocks the active site unique for bacteria;therefore, penicillin is a poison for bacteria but not human.

8: Why do we need vitamin? (Imagine this is a Plattners type of 4-5 marks testquestion and you lose marks severely if you are missing points.)A: Vitamins are:1) Components of coenzymes2) Required in trace amounts in our diet and in diets of other animals for synthesiscoenzymes that affect health and physical fitness3) Becomes part of the coenzymes molecular structure.

6.4 Oxidation-Reduction and the Flow of Energy

The redox reaction Oxidationis the lossof

elections Reductionis the gainof

electrons In cells, redox reactions

often involve the oxidationof substrates by removal ofhydrogen atoms and thereduction of others by the

gain of hydrogen atoms.

Photosynthesis A REDUCTION (gain electron) reaction Carbon dioxide is reducedto glucose and water is oxidized to oxygen. Reduction

of carbon dioxide to form a mole of glucose stores 686 kcal in the chemicalbonds of glucose.


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Cellular Respiration An OXIDATION (lose electron) reaction Glucose is oxidizedto carbon dioxide and oxygen is reduced to water. The

oxidation of a mole of glucose releases 686kcal in energy and this is used tosynthesize ATP.

Organelles and the flow of energy Chloroplasts capture the energy of the sun and carry on photosynthesisto

produce carbohydrates. Mitochondria carry out aerobic cellular respirationthat break glucose down; the

energy released produces ATP molecules.

Cycling molecules between chloroplasts and mitochondria allows a flow ofenergy from the sun through all living things.

bio 12 chapter 6 metabolism notes

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